When fuel costs are high, the demand for high power or high performance vehicles typically decreases in favor of more fuel efficient vehicles. Adding or combining technologies, such as diesel combustion, turbo charging, and supercharging, can result in increases in fuel economy with minimal sacrifice in power and performance. Variable displacement engine systems have been introduced to address the balance between high power or performance and fuel efficiency by automatically deactivating banks or opposing pairs of cylinders during low-demand operation, such as highway cruising, and reactivating the cylinders during high-demand operation, such as when passing on the highway or accelerating from a stop.
One of the first variable displacement systems was developed by General Motors in the early 1990's and was called Displacement on Demand (OD). The DOD system was first used in the Cadillac L62 “V8-6-4” engine, in which opposite pairs of cylinders could be turned off and on allowing the engine to have three different modes of operation, i.e. 8, 6 and 4 cylinders. The DOD system proved to be troublesome and was retired after a short production run due to a poor service record.
Similar approaches were used by Chrysler in its Hemi V8 engine (Multiple Displacement System or “MDS”), by Mercedes in its 600 series 5.8L V12 engine (Active Cylinder Control or “ACC”), and by Honda in its i-VTEC 3.5L V6 engine (Variable Cylinder Management or “VCM”).
It remains desirable to provide a mechanism for deactivating and reactivating valves on-demand that improves over previous variable displacement designs in terms of performance, efficiency and robustness.